1.1 This International Standard describes the calculation of mass flow for sizing pressure relief devices for parts of refrigerating systems. NOTE The term "refrigerating system" used in this International Standard includes heat pumps. 1.2 This International Standard describes the calculation of discharge capacities for pressure relief valves and other pressure relief devices in refrigerating systems including the necessary data for sizing these when relieving to atmosphere or to part of the refrigerating system at lower pressure. 1.3 This International Standard specifies the requirements for selection of pressure relief devices to prevent excessive pressure due to internal and external heat sources, the sources of increasing pressure (e.g. compressor, heaters, etc.) and thermal expansion of trapped liquid. 1.4 This International Standard describes the calculation of the pressure loss in the inlet and outlet lines of pressure relief valves and other pressure relief devices and includes the necessary data.